1. Field of the Invention
The present invention relates generally to lehrs for heating and forming glass sheets and, more specifically, to a block assembly for a gas-type lehr.
2. Description of the Related Art
It is known to heat and form glass sheets using a "hearth" or "lehr". Generally, the lehr is a furnace and may be of a continuous roller-type, fixtured roller-type or gas-type. For example, a gas-type lehr has a plurality of blocks disposed beneath a plurality of radiant heaters. Each block is supported along its transverse sides by refractory slabs or support lintels mounted upon jacks. Typically, four jacks are used for each block with two jacks, one at each longitudinal end, for each lintel. The jacks are adjustable, thereby making possible manual adjustment of the vertical location of each block so that upper surfaces of the blocks can be brought into alignment with each other.
In operation of the gas-type lehr, a glass sheet is placed inside the lehr where it is heated by conventional radiation, convection and conduction heat. The glass sheet is moved along the blocks at a predetermined rate which depends on the thermal conductivity of the glass sheet to reach a temperature in its forming range. When the glass sheet is at a temperature in its forming range, the glass sheet is formed to a predetermined shape of the blocks. Once formed, the glass sheet is either quenched, annealed or tempered.
Although the above lehr has worked well, it suffers from the disadvantage that the alignment of a top contour or upper surface of the blocks is required for correctly forming the glass sheet. This requires extensive adjustment and alignment of the blocks inside the lehr which is labor intensive and costly. Another disadvantage of the above lehr is that seals are required between the longitudinal ends of the blocks which requires a separate part and is costly. As a result, there is a need in the art to provide a block assembly for alignment of the blocks prior to installation inside the lehr and to reduce or eliminate adjustment of the blocks inside the lehr.